Mammals are protected from the outside environment by a barrier consisting of the skin, which is a highly structured tissue composed of several layers, but sensitive to attacks due to the variations in the extracorporeal environment. This situation is unique in the animal kingdom since fish and frogs secrete mucus, birds are covered with feathers, and submammalian and mammalian vertebrates, except current Hominidae, are covered with hair.
Humans have lost these protective attributes: they have a skin which must be protected and which can be stimulated in order to help it to combat attacks and aging.
In particular, it is known that aging is a physiological phenomenon which results in particular in thinning of the skin and a loss of elasticity, leading in particular to the appearance of more or less deep wrinkles. Loosening or drying-out of the surface and anarchic pigmentation may also be observed.
The skin comprises three layers: the epidermis, the dermis and, deep down, the hypodermis.
The outermost protective envelope of the skin, the epidermis, which tightly covers the dermis, consists, at the surface, of the stratum corneum. The stratum corneum is made of two layers: the stratum disjunctum at the surface, the particularity of which is desquamation, and the stratum compactum, the deepest, which plays the role of a barrier. The epidermis, which is easy to observe macroscopically since it is at the surface, has been the subject of many studies. Known responses are those caused by certain agents of the extracorporeal environment or those resulting from the application of active substances of diverse origins. The cells of the epidermis result from the activity of the cells of the basal layer which lies on a basal membrane separating the epidermis from the dermis.
The dermis results from the biosynthetic activity of fibroblasts, which produce the constituents of the extracellular matrix. The latter is made up of four major families of macromolecules: collagens, elastin, structural glycoproteins and proteoglycans. The dermis has the ability to respond to the signals given out by the epidermis, which, in response, also sends signals to the epidermis. In general, exchanges exist between these various dermal and epidermal layers of the skin, which are intended to ensure cell renewal and the cohesion and moisturization of the outer layers.
Many active agents have been proposed for preventing or delaying the effects of aging.
Among these, mother-of-pearl has been used since the beginning of time in aesthetics and in conventional pharmacopeiae. Moreover, mother-of-pearl is known for its bone-regenerating properties.
It is in particular known that mother-of-pearl, or conchiferous aragonite, is a biogenic mineralized formation; it consists of an organic matrix of fibrous and nonfibrous substances representing approximately 1.7 to 2% of the total mass (Taylor et al, Bulletin of the British Museum (Natural history) Zoology. Suppl. 3125 pp.+29 Plates, 1969) and of calcium carbonate crystallized in orthorhombic form, named aragonite, combined with trace elements (sodium, magnesium, lanthanum, zinc, bromine, cesium, iron, manganese, chlorine, copper, potassium, calcium, strontium and sulfur). More particularly, the entire organic phase of mother-of-pearl is in the form of an organic matrix composed of fibrous proteins, consisting in particular of ancestral collagens lacking hydroxyproline and hydroxylysine, and of nonfibrous proteins. Approximately 50% of the organic matrix of mother-of-pearl is water-soluble. The remaining 50% can only be obtained after decalcification.
However, the products of the prior art, obtained by mixing a mother-of-pearl powder with a pulverulent, inert diluent or excipient, as described, for example, in application WO 97/23231, cause undesirable phenomena of skin irritation, due to the presence of the mother-of-pearl in the form of powder (in particular of its major component, aragonite or CaCO3). It is therefore imperative that the content of mother-of-pearl powder in these products should be very limited in order to avoid these irritation phenomena. These undesirable phenomena of irritation are in particular caused by the pH, which is too basic, of these known products, in contact with the skin. In addition, the known products based on mother-of-pearl powder have specific formulation problems, in particular stability (breaking of emulsions) and of adjustment of the pH to a less basic value.
Moreover, application WO 97/24133 describes a method for preparing biologically active substances from mother-of-pearl, by bringing a mother-of-pearl powder into contact with an aqueous solvent chosen from pure, double-distilled or apyrogenic water, optionally supplemented with salts, from which the water-soluble fraction is then separated so as to recover only the aqueous fraction, therefore essentially lacking the water-insoluble organic phase and inorganic components of mother-of-pearl. This method cannot therefore enable, in particular, the preparation of a composition comprising in particular all of the components of mother-of-pearl, particularly the entire organic phase of mother-of-pearl.